<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <div>
        <button id="btn">点击</button>
    </div>

    <script>
        document.getElementById("btn").onclick = function() {
            console.log("按钮被点击了");
        }
    </script>
</body>

</html>